Interests in renewable and sustainably producible new environmentally-friendly carbon resources have grown as the possibility of depletion of fossil fuels has increased. Among these resources, ethanol obtained through the fermentation of plants has been mass-produced in Brazil and the United States of America, and the ethanol has already been used as transportation energy in a number of developed countries and developing countries including the above countries.
Ethanol may not only be used as a possible alternative energy source, but may also be used in the preparation of various olefins including ethylene, as a basic raw material of petrochemical industry, through dehydration. A high-yield ethylene conversion reaction by the dehydration of ethanol is an endothermic reaction and the corresponding process may be regarded as an energy-intensive process in which a lot of heat is consumed for the pretreatment of raw materials and the removal of impurities in reactants and products. Thus, there is a need to design an energy-efficient catalytic process capable of producing ethylene in high yield at low temperature.
In general, alumina basic catalysts have been used as a commercially used catalyst for the dehydration of ethanol, and the production of ethylene is performed in a high temperature range of 300° C. to 500° C. This may require a lot of heat for the adjustment of reaction temperature and the preheating of raw materials and may cause a lot of costs and limitations due to high-temperature, high-pressure operation and design. Also, even if the production of ethylene in high yield is possible, in a case in which ethanol conversion rate and ethylene selectivity in a particular temperature region are not simultaneously secured by 98% or more, the performance of the catalyst may not only be degraded, but also additional costs due to a post-treatment purification process using ethylene as a raw material may be incurred and the purity of the product may be reduced.
Korean Patent No. 0891001 discloses a method of preparing a ZSM-5/SAPO-34 composite catalyst by mixing crystalline ZSM-5 obtained by hydrothermal synthesis in a preparation process of SAPO-34 and performing a series of processes of hydrothermal synthesis and sintering, and a method of preparing light olefin, which may maintain a selectivity of C2-C4 light olefin of 70 carbon mole % or more and a selectivity ratio [C3/C2] of propylene to ethylene of 1.0 or more by performing a reaction converting an oxygen-containing compound to light olefin in the presence of the ZSM-5/SAPO-34 composite catalyst obtained by the above method.
Korean Patent No. 1085046 relates to a method of preparing C2-C4 light olefins from an oxygen-containing compound, such as methanol and dimethyl ether, in the presence of a mordenite catalyst, wherein the patent discloses a method of preparing light olefin in which propylene and butene may be obtained in a yield of 60 wt % or more and, in particular, butene may be obtained in a high yield of about 30 wt %.
Korean Patent Application Laid-Open Publication No. 2011-0043878 discloses a method of preparing a microspherical SAPO-34 catalyst by preparing microspheres by spray drying a mixed slurry including a crystallized undried SAPO-34 slurry, a binder, and an additive, and then sintering the microspheres, and a catalyst having excellent reactivity as well as high strength, as a microspherical SAPO-34 catalyst for a circulating fluidized bed reactor which is prepared by the above method.
Non-Patent Document 1 (Dongsheng Zhang, Rijie Wang, Xiaoxia Yang, Effect of P Content on the catalytic performance of P-modified HZSM-5 Catalysts in dehydration of Ethanol to ethylene, Catalyst Letter 124, 384-391 (2008)) is a paper related to dehydration effect of a P-modified H-ZSM-5 zeolite catalyst in which a H-ZSM-5 catalyst is impregnated with phosphorus (P), wherein experiments on the conversion of ethanol to ethylene using the P-modified H-ZSM-5 catalyst at various temperatures have been conducted. In this paper, since ethylene is mainly produced at 573 K to 713 K with respect to a catalyst having a phosphorous content of 3.4 wt % or more and ethylene and high hydrocarbons (C3-C9+aliphatic and aromatic) are produced at high temperature with respect to a catalyst having a phosphorous content of 3.4 wt % or less, it may be understood that high-temperature dehydration of the catalyst is an essential reaction to enable the conversion of ethanol to ethylene in the presence of the catalyst having a phosphorous content of 3.4 wt % or more.
With respect to the catalysts disclosed in these patents and non-patent document, the yield of ethylene is relatively low, there is a limitation in that high-purity ethylene is not selectively produced, and it may be referred to as an inefficient process in which high energy is consumed for the high-temperature reaction.
U.S. Pat. No. 4,873,392 discloses a catalyst for conversion of ethanol to ethylene, as a lanthanum-modified H-ZSM-catalyst, in which catalytic activity at low temperature is improved. In the patent, although the possibility of the activity of the ethanol dehydration catalyst in a relatively low-temperature region has been suggested, there is a limitation in that very low space velocity (weight hourly space velocity (WHSV)) is required to exhibit significant catalytic activity and the yield of ethylene is also not satisfactory.
Non-Patent Document 2 (Nina Zhan, Yi Hu, Heng Li, Dinghua Yu, Yuwang Han, He Huang, Lanthanum-Phosphorous modified HZSM-5 catalysts in dehydration of ethanol to ethylene: A comparative analysis, Catalysis Communications 11, 633-637 (2010)) is a paper related to a method of preparing ethylene from hydrous ethanol using a ZSM-5 catalyst in which lanthanum and phosphorous are simultaneously impregnated, wherein the catalyst, in which lanthanum and phosphorous are simultaneously impregnated, has an effect of preventing the loss of alumina in a ZSM-5 catalyst skeleton according to the supply of a raw material having a high water content, but the activity may be reduced when a raw material having a high ethanol content is used and the reaction temperature may be set to a high temperature in order to address this issue.
Some prior art documents suggest examples of using catalysts in which gallium is introduced into zeolite.
In Non-Patent Document 3 (F. J. Machadoa, C. M. Lopez, Y. Camposa, A. Bolivar, S. Yunes, The transformation of n-butane over Ga/SAPO-11, The role of extra-framework gallium species, Applied Catalysis A: General, 226, 241-252 (2002)), a zeolite catalyst having gallium introduced thereinto, as a dehydrogenation catalyst required for the preparation of isobutene from normal butane, was used in the preparation of olefin. In this paper, it is reported that when the zeolite catalyst, to which gallium was added, was used as a catalyst under atmospheric pressure and relatively high temperature reaction condition, i.e., 500° C., the selectivity of isobutene among products was improved through the dehydrogenation of normal butane. Specifically, the used catalysts included SAPO-11, as a starting catalyst, and a catalyst in which gallium was introduced in an amount of 0.25 wt % to 2.2 wt %. However, since an olefin compound was prepared by using a hydrocarbon compound, instead of alcohol, as a raw material, it is reported that the reaction followed a mechanism (reaction mechanism) of dehydrogenation instead of dehydration and the selectivity of olefin was improved at a high temperature of 500° C.
In Non-Patent Document 4 (R. Barthos, A. Szechenyi, and F. Solymosi/Decomposition and Aromatization of Ethanol on ZSM-Based Catalysts/J. Phys. Chem. B/110, 21816-21825 (2006)), research into the characteristics of a catalyst related to the improvement of the selectivity of an aromatic compound was conducted by using a raw material to which ethanol or ethylene was added. Although the research resulted in screening a catalyst having excellent selectivity in the preparation of the aromatic compound at a high temperature of 500° C. to 600° C. among catalysts prepared by using H-ZSM5 as a starting catalyst and adding a metal (molybdenum, rhenium, zinc, gallium, etc.) in an amount of 2 wt %, research into the improvement of the selectivity and yield of ethylene obtained as a final product from the dehydration of ethanol was not conducted.
Non-Patent Document 5 (A. Ausavasukhi, T. Sooknoi/Additional Brønsted acid sites in [Ga]HZSM-5 formed by the presence of water/Applied Catalysis A: General/361, 93-98 (2009)) also reports research results similar to those of Non-Patent Document 2. However, experimental results suggested that the yield of aromatic compound was improved when a catalyst hydrothermally treated with 1 wt % of steam at 425° C. was used or water was directly added to a reactant stream in the preparation of Ga-ZSM-5 by adding 3 wt % of gallium.
With respect to these non-patent documents, since alcohols were not used as a reactant or ethylene was not a desired reaction product, it may be considered that these documents are significantly different from the scope of the present invention to be later described, i.e., an efficient catalytic reaction usable in the preparation of ethylene through the dehydration of ethanol, in terms of technical objectives as well as a chemical route. The catalysts prepared according to the methods suggested in these documents may be ineffective or may have very limited selectivity or yield of ethylene when ethylene is prepared through the dehydration of ethanol.